The present invention relates to a structure of a light emitting diode (LED) and a method of making the same, and more particularly, to a structure of a light emitting diode with the P electrode and the N electrode mutually intercrossed, and a method of making the same.
In recent years, a great deal of attention has been directed to the light-emitting device utilizing gallium nitride-based semiconductors such as GaN, AlGaN, InGaN, and AlInGaN. Usually, most of the light-emitting devices of the aforementioned type are grown on an electrically insulating sapphire substrate, which is different from other light-emitting devices utilizing a conductive substrate. Since the sapphire substrate is an insulator, the electrodes cannot be directly formed on the substrate directly, and has to directly contact the P-type semiconductor layer and the N-type semiconductor layer individually so as to complete the manufacturing of the light-emitting device formed on the sapphire substrate.
Please refer to FIG. 1 and FIG. 2, wherein FIG. 1 is a diagram showing the top view of the conventional light emitting diode made from the gallium nitride-based semiconductor, and FIG. 2 is a diagram showing the cross-sectional view taken from the a-axe2x80x2 line in FIG. 1. Such as shown in FIG. 1 and FIG. 2, an N-type GaN layer 20, an active layer 40, a P-type GaN layer 60, and a transparent contact layer 80 are sequentially formed as a stacked structure on a sapphire substrate 10. The aforementioned active layer 40 is made of GaN, AlGaN, InGaN, or AlInGaN having a double hetero-junction structure or a quantum well structure. Thereafter, an etching process is performed to expose a portion of the N-type GaN layer 20. Then the N electrode 70 and the P electrode 90 are formed respectively on the exposed surface of the N-type GaN layer 20 and on the surface of the transparent contact layer 80.
The aforementioned FIG. 1 and FIG. 2 show the conventional light emitting diode made from the gallium nitride-based semiconductor with small chip size. Generally, the actual size of such light emitting diode with small chip size is 10 milxc3x9710 mil, or 8 milxc3x978 mil. When the size of the light emitting diode is larger than 10 milxc3x9710 mil, such as 20 milxc3x9720 mil (i.e. the area is 400 mil2), such light emitting diode belongs to the category of big chip size.
The sizes of P electrode and N electrode of the conventional light emitting diode with big chip size are not enlarged in accordance with the chip size. The reason resides in that the P electrode and the N electrode have the nature of blocking light. Hence, if the size of P electrode and that of the N electrode are enlarged as the size of the chip is enlarged, the light emitting efficiency of the light emitting diode with big chip size will be reduced. Therefore the conventional light emitting diode with big chip size utilizes another method for designing the P electrode and the N electrode. Please refer to FIG. 3, wherein FIG. 3 shows the top view of the conventional light emitting diode with big chip size. Since FIG. 3 merely shows the top view, only part of the elements of the conventional light emitting diode with big chip size can be illustrated in FIG. 3. Those elements shown in FIG. 3 are an N-type GaN layer 120, an N electrode 170, a transparent contact layer 180, and P electrode 190 wherein the N electrode 170 is located on a portion of the N-type GaN layer 120; the transparent contact layer 180 is located on another portion of the N-type GaN layer 120; and the P electrode 190 is located on the transparent contact layer 180. Moreover, in FIG. 3, an N pad 175 and a P pad 195 are further used as contacts for use in the connection of external wiring.
According FIG. 3, the conventional light emitting diode with big chip size is featured in a plurality of striped N electrodes 170 and P electrodes 190, and any two stripes of N electrodes 170 and P electrodes 190 are not mutually intercrossed. Besides this method can prevent the serious light blocking caused by the too large total electrode area, it can promote the evenness of current distribution. However, although this design has its own merits, yet its size is fixed, so that it lacks of the possibility for change in accordance with the actual demands.
Just as described above, the design of the conventional light emitting diode with big chip size still has room for improvement. Hence, an objective of the present invention is to provide a structure of a light emitting diode and a method of making the same, wherein the structure design is based on a unit chip, whereby the light emitted by each unit chip is more even and the operating voltage of the device is reduced.
Another objective of the present invention is to provide a structure of a light emitting diode and a method of making the same wherein all the P electrodes and the N electrodes on the wafer are respectively connected in series, whereby the cut size of the device can be enlarged arbitrarily according to the size of the unit chip.
Still another objective of the present invention is to provide a structure of a light emitting diode and a method of making the same, whereby the light emitting efficiency is increased.
According to the aforementioned objectives of the present invention, the present invention provides a structure of a light emitting diode comprising: a substrate; a semiconductor epitaxial structure comprising an N-type semiconductor layer, an active layer, and a P-type semiconductor layer, wherein the N-type semiconductor layer covers the substrate, and a plurality of extrusions are formed on a portion of a surface of the N-type semiconductor layer, and a channel is formed between every two adjacent extrusions, and the active layer and the P-type semiconductor layer are stacked in sequence on the extrusions; an N-type electrode layer which adheres to the N-type semiconductor layer and is located in the channel; and a plurality of P-type electrodes located above the P-type semiconductor layer. Moreover, the structure of the light emitting diode according to the present invention further comprises a transparent contact layer located between the P-type semiconductor layer and the P-type electrodes. Furthermore, the structure of the light emitting diode according to the present invention further comprises an insulating layer covering the transparent contact layer and the N-type electrodes, wherein a portion of the N-type electrode layer is exposed to be an N-type pad; and a conductive layer that covers the insulating layer and is connected to the P-type electrodes, wherein at least one P-type electrode of the P-type electrodes is a P-type pad.
Furthermore, according to the aforementioned objectives of the present invention, the present invention provides a method of making the above structure of a light emitting diode. The method comprises the following steps: firstly, providing a substrate; then, forming an N-type semiconductor layer covering the substrate, wherein a plurality of extrusions are formed on a portion of a surface of the N-type semiconductor layer and a channel is formed between every two adjacent extrusions; then, forming an active layer covering the extrusions; then, forming a P-type semiconductor layer covering the active layer; then, forming a transparent contact layer covering the P-type semiconductor layer; then, forming an N-type electrode layer which adheres to the N-type semiconductor layer and is located in the channel; then, forming a plurality of P-type electrodes adhering to a portion of a surface of the transparent contact layer; then, forming an insulating layer covering the transparent contact layer and the N-type electrodes, wherein a portion of the N-type electrode layer is exposed to be an N-type pad; and then forming a conductive layer which covers the insulating layer and is connected to the P-type electrodes, wherein at least one P-type electrode of the P-type electrodes is a P-type pad.